1. Field of the Invention
The present invention relates to a differential gear for a motor vehicle, comprising a casing, an input shaft which can be coupled to a drive shaft of the motor vehicle, two output shafts which are arranged approximately perpendicular to the input shaft, each of said output shaft being couplable to a wheel of the motor vehicle, and a differential supported within the casing, wherein the casing comprises two casing parts, each of the casing parts comprising an attachment spot for attaching the casing to a body of the motor vehicle, said two casing parts being connected to each other along a separation plane, said separation plane being oriented with respect to the output shafts at an angle of more than 40 degrees.
2. Description of the Prior Art
A differential gear for motor vehicles, as mentioned above, is known for instance from L. R. Buckendale (U.S. Pat. No. 2,478,1809).
Differential gears of this type are typically used in motor vehicles having a conventional drive, i.e. the motor in the front and driven wheels at the rear. The differential gear is arranged between the two rear wheels of the motor vehicle.
The differential contained within the differential gear allows that the two rear wheels can have different speeds, e.g. when driving a turn.
The casing, in modern differential gears, includes typically a main casing and a casing lid, as is known for instance from A. Stephan et al. and from W. Naumann (German patent application publications No. 36 26 442 and 1 801 917, respectively). Attachment spots for attaching the casing to the body of the motor vehicle are typically provided at the lid, in some cases at the main casing, in some cases at both said casing parts.
In such modern differential gears, the main casing is usually provided at its front end with an opening for bearing the input shaft, and is provided at its rear end with a mounting opening which can be closed by means of the lid. The differential is mounted via the mounting opening.
The separation line between the main casing and the casing lid is usually flat and sealed by means of a seal. The seal can be a fluid, a flat or a shaped seal. The separation line of differential gears as are known from A. Stephan et al. is arranged within a separation plane which is essentially parallel to the output shafts.
In contrast thereto, the separation plane of the separation line of the differential gear of Buckendale is arranged approximately perpendicular to the output shafts.
In the above-mentioned German document 1 801 917 of Naumann, it is suggested to provide a differential gear having a main casing and a casing lid with a separation line parallel to the output shafts, wherein an oil collection space is provided within the lid. The oil collection space is open at its top end and is connected to the main space of the casing via an opening. During the operation of the differential gear, oil is thrown into the collection space. The opening is provided such that the main cavity is filled with oil up to a sufficient level, said level being such that losses due to splashing and thus the oil temperature do not rise excessively.
A similar concept is known from Ralph W. Baxter (U.S. Pat. No. 5,709,135). The casing of the differential gear of Baxter has two parts which are separated like a clam, having a horizontal separation line. A reservoir is provided in the lower casing part, in a region where the input shaft enters the casing. The oil is thrown into the reservoir by a ring gear of the differential. There is no disclosure on how the casing of the differential gear is attached to the body of the vehicle.
Finally, C. Alt (German patent publication 196 24 002) discloses a multispot support of a differential gear. The casing of the differential gear comprises a main casing and a casing lid, a separation plane being parallel to the output shafts. The main casing and the casing lid are provided with attachment spots at cantilever arms which project from the casing of the differential gear. The cantilever arms may be formed integrally with the casing of the differential gear, and may have a hollow cross section.
It is an object of the present invention to provide an improved differential gear for a motor vehicle.
It is another object of the present invention to provide a differential gear that can be easily attached.
It is another object of the present invention to provide a differential gear that can be easily manufactured.
Still a further object of the invention is to provide a differential gear having a good efficiency.
It is another object of the present invention to provide a differential gear having a simple construction.
These and other objects are achieved by a differential gear for a motor vehicle, comprising:
a casing,
an input shaft which can be coupled to a drive shaft of the motor vehicle,
two output shafts which are arranged approximately perpendicular to the input shaft and which can be connected to a respective wheel of the motor vehicle, and
a differential supported within the casing, wherein the casing comprises two casing parts, each of the casing parts comprising an attachment spot for attaching the casing to a body of the motor vehicle, said two casing parts being connected to each other along a separation plane which is oriented at an angle of more than 40 degrees with respect to the output shafts, wherein at least one of said two casing parts comprises a projection which serves as a hollow carrier, said projection comprising an attachment spot for attaching the casing at its outside, said projection being arranged generally parallel with respect to the output shafts, and said projection being arranged above a rest oil level within the casing, wherein a retaining element is arranged within the casing at the entrance of the projection, said retaining element limiting the flow of oil back into the casing which has been thrown into the projection.
In view of the fact that the separation plane is arranged obliquely or perpendicular with respect to output shafts, a number of advantages arise. Particularly, the differential gear can be easily attached and the degree of freedom with respect to the shape of the casing is increased.
Such construction of the casing allows that the rigidity of the casing is constant in a direction around the axis of the output shafts, to the farest possible extent. Thus, the bias of the differential gear bearings in the casing can be made uniform around the circumference thereof.
A projection oriented in parallel to the output shafts can be easily realized due to the arrangement of the separation plane, even if the casing parts are molded.
In view of the fact that the projection is provided within the casing above the rest oil level, the projection can be used at high speeds for taking up oil which is thrown into the projection by the action of the differential which is supported within the casing, particularly by means of the ring gear thereof. Thus, the oil level decreases and the losses due to splashing are decreased, leading to less generation of heat. Thus, the efficiency is improved.
Due to the retaining element which is arranged at the entrance of the projection, any backflow of oil that has been thrown into the projection, into the casing is limited. Thus, only a limited amount of oil per time unit can flow back from the projection, wherein this oil amount is at high speeds lower than the amount of oil that is thrown per this time unit into the projection. Thus, at high speeds, oil is retained within the projection, i.e. within the cavity formed by the projection. At lower speed and high torque, the feeding effect is decreased and less amount of oil is retained within the projection. Thus, the entire oil volume can be used for lubrication and cooling purposes.
In view of the fact that an attachment spot for attaching the casing is provided at the outside of the projection, the projection serves as a hollow carrier. By using the projection as hollow carrier, a rigid connection of the attachment spot for attaching the casing is possible.
In a preferred embodiment, the separation plane is arranged approximately perpendicular to the output shafts.
Thereby, it is particularly easy to mount the differential in one of the two casing parts.
Further, it is preferred if the retaining element is a retaining sheet which is fixed at the entrance of the projection. Thereby, the retaining element can be manufactured and mounted at low cost.
In another preferred embodiment, the two casing parts are formfittingly connected to each other in a direction transverse to the orientation of the output shafts. Thereby, bearing forces of the differential are transferred via the form-fit connection (positive engagement), said connection being for instance a centering collar.
In addition, it is preferred if the two casing parts are sealed with respect to each other by means of an O-ring seal. Such a seal can be realized at low cost, particularly if the casing parts are form-fittingly connected to each other in a direction transverse to the orientation of the output shafts.
According to another preferred embodiment, the two casing parts are made of a light-weight material, preferably from a magnesium alloy or aluminum alloy.
In view of the fact that the casing rigidity is maintained essentially uniformly around the differential axis, i.e. around the axis of the output shafts, it is possible to use a lightweight material for the casing of the differential gear. The higher bias that is necessary to be imparted upon the differential bearings, is transferred uniformly to the circumference of these bearings.
It will be appreciated that the features mentioned above and the features that will be described below, cannot only be used in the respective quoted combination, but also in other combinations or, on their own, without departing from the scope of the present invention.